Injection molding is commonly used to produce containers. One popular container produced in large quantities by such method is the five gallon pail (not shown). Commonly, the pail is provided with a peripheral flange which circumscribes the open upper end of the pail and extends therefrom outwardly or radially (not shown).
Lids are often also produced. One prior art lid 20 is shown in cross section in FIG. 1. This lid 20 has a main body portion 22, a depending annular peripheral skirt 24 and an inwardly disposed locking flange 26 which circumscribes the interior of the skirt 24. This permits the lid 20 to be snap-fit over the open end of a pail, such that the locking flange 26 mechanically engages the underside of the peripheral flange thereof (not shown). To facilitate pouring, in situations wherein the lid 20 is used with liquids or other pourable material, its main body portion 22 has a central planar portion 28 and a tubular spout portion 30. The central planar portion 28 defines an aperture 32. The spout portion 30 has one end 34 in communication with the aperture 32 and extends therefrom, in a direction opposite to the direction in which the skirt 24 depends, to a distal end 36. To facilitate sealing, it is common to provide the main body portion 22 with a rim portion 38 which circumscribes the distal end 36 of the spout portion 30 and radially projects therefrom, and to provide a cap (not shown) which can be crimped around the distal end 36 to mechanically engage the underside of the rim portion 38. For reasons evident from the foregoing, the aforedescribed type of lid is known in the industry as one having a “crimp-on pour spout”.
A number of known systems are used to mold lids having crimp-on pour spouts.
One known system is illustrated in FIGS. 2,2A. This system includes a core mold 40 which forms the underside of the lid and the inner surface of the pour spout, a stripper ring 42 which forms the lower edge of the skirt, and a cavity mold 44 which forms the top surface of the lid. In operation, after a lid has been molded, the cavity mold 44 separates from the core mold 40 and stripper ring 42, leaving the lid in place, and thereafter, the stripper ring 42 separates from the core mold 40, to eject the lid 20, as shown in FIG. 2A. This system is known to be capable of the economic production of lids, but suffers from being relatively noisy during mold use, and also results in distortion of the spout and other high-stress areas during separation.
Another known system is shown in FIGS. 3A,3B,4A,4B. This system includes a core mold 40′ which forms the underside of the lid and the inner surface of the pour spout, a stripper ring 42′ which forms the edge of the skirt, and a cavity mold 44′ which forms the top surface of the lid. A ring of collets 46 form part of the cavity mold 44′. In operation, after a lid has been molded, the cavity mold 44′ separates from the core mold 40′ and stripper ring 42′, leaving the lid. During such process, the collets 46 move out and away from another. The stripper ring 42′ thereafter separates from the core mold 40′, to eject the lid, as shown in FIG. 4B. This system is known to be capable of producing molded parts of good quality. However, the system, being relatively mechanically complex, can suffer from relatively high expense. Further, the edges where the collets meet can leave witness lines on the molded part. As well, unless the collets are provided with cooling, which adds yet further complexity and cost, the cycle time can be relatively slow (which itself has an associated cost) and the molded parts can suffer from excessive distortion.